Method and apparatus for locating improperly positioned or bent rolls

ABSTRACT

A method and apparatus for locating improperly positioned or bent rolls among a set of rolls which define a confined path of travel for a workpiece, particularly useful for checking a straight or curved roll-rack of a continuous-casting machine. The apparatus may be propelled through the path defined by the rolls by any suitable mechanism. For example, as applied to a roll-rack, the apparatus may be attached to the upper end of a starter bar and propelled with the bar through the rack, or the apparatus may be suspended from a hoist and pulled through the rack. The apparatus includes a housing and means within the housing for measuring the gap between work-engaging faces of the rolls and-or, when used with a curved roll-rack, means for measuring the angular relation of adjacent bottom rolls. The latter measurement is used in determining whether the work-engaging faces lie on arcs of the intended radii. Bent rolls are located by observing different measurements when the apparatus is moved in opposite directions through the path of travel.

This invention relates to an improved method and apparatus for locatingimproperly positioned or bent rolls among a set of rolls which define aconfined path of travel for a workpiece. In referring to rolls as"improperly positioned," we mean that the gap between the work-engagingfaces of two rolls of an opposed pair may not be of the properdimension, or that the work-engaging faces may not lie on an intendedarc.

Although our invention is not thus limited, our method and apparatus areparticularly useful for locating improperly positioned or bent rolls ina roll-rack of a continuous-casting machine. A conventional curved orstraight roll-rack includes a frame and a plurality of opposed pairs ofrolls journaled in the frame for guiding and confining a casting as itscore continues to solidify. A curved roll-rack includes top and bottomrolls which guide a casting as its direction of travel changes fromsubstantially vertical to horizontal. A curved roll-rack usually definesan arcuate path of travel of a radius of at least about 30 feet. The gapbetween the work-engaging faces of the roll-pairs depends on thethickness of the casting, but seldom is less than about 6 inches.Consequently a curved roll-rack is a massive mechanism, yet it isimportant that its rolls all are straight and positioned accurately. Thework-engaging faces of the top and bottom rolls of each pair should lieaccurately on two predetermined arcs. In either a straight or curvedroll-rack the gaps between the work-engaging faces of each roll-pairshould be equal within small tolerances. Any rolls which are bent or notpositioned properly may either become overloaded and hence subject toearly failure, or else they do not effectively confine the casting.

In most continuous-casting installations the gaps between roll faces aremeasured manually and the rolls are adjusted with shims only while thecasting machine is down for scheduled maintenance, ideally about oneturn a week. Measuring and adjusting the roll gaps manually are awkwardoperations, often done inaccurately. An improperly gapped roll-pair maygo unnoticed until the next scheduled maintenance unless an actualfailure occurs. As far as we are aware, there has been no satisfactoryway of locating bent rolls nor of determining whether or not thework-engaging faces of a curved roll-rack lie accurately on arcs of theintended radii.

An object of our invention is to provide an improved method andapparatus, particularly useful for continuous-casting machines, forexpeditiously checking or determining whether rolls which define aconfined path of travel for a workpiece are positioned properly and forlocating any improperly positioned or bent rolls.

A further object is to provide an improved method and apparatus which,as applied to a curved roll-rack, enable us both to measure the gapsbetween the work-engaging faces of the roll-pairs and to determinewhether these faces lie on arcs of the intended radii, or to performeither operation independently of the other.

A further object is to provide an improved method and apparatus foraccomplishing the foregoing objects, the apparatus of which includes ahousing movable through the path defined by the work-engaging faces ofthe roll-pairs, said housing carrying gap sensors and/or angle sensorsfor contacting the individual rolls and means for transmitting signalsindicative of the gap measurements and/or angle measurements.

A more specific object is to provide an improved method and apparatusfor accomplishing the last-named object in which the housing can bemounted on the starter bar of a continuous-casting machine and propelledwith the starter bar along the path defined by the work-engaging facesof the roll-pairs of a roll-rack.

A further object is to provide an improved method and apparatus forlocating bent rolls, as well as improperly positioned rolls, in whichbent rolls are indicated when the gap measurements differ as theapparatus moves in opposite directions through the path defined by therolls, or when the gap between the work-engaging faces of a roll-pairvaries significantly along the length of the rolls.

In the drawings:

FIG. 1 is a diagrammatic side elevational view of an illustrative formof continuous-casting machine with our apparatus installed therein;

FIG. 2 is a front elevational view of our apparatus with parts brokenaway;

FIG. 3 is a side elevational view of our apparatus with parts brokenaway;

FIG. 4 is a horizontal section on a larger scale on line IV--IV of FIG.3;

FIG. 5 is a simplified wiring diagram of the gap-measuring circuitembodied in our apparatus;

FIG. 6 is an example of a recorded gap measurement obtained with ourapparatus;

FIG. 7 is a simplified wiring diagram of the circuit embodies in ourapparatus for measuring the angles of lines tangent to the work-engagingfaces of the rolls and thereby determining whether these faces lie onarcs of the intended radii; and

FIG. 8 is an exaggerated diagram illustrating the geometric principlesinvolved in using the angle measurement to check the radius of an arc.

EXAMPLE OF CONTINUOUS-CASTING MACHINE

The principles of our invention may be applied generally for locatingimproperly positioned or bent rolls among a set of rolls which define aconfined path of travel for a workpiece. For illustrative purposes only,we shown our invention used with a curved roll-rack of acontinuous-casting machine. The continuous-casting machine illustratedis constructed as shown in Bode and Wrhen U.S. Pat. No. 3,735,848 and inGallucci and Slamar U.S. Pat. No. 3,752,210, both of common ownership.

As shown in FIG. 1, the casting machine illustrated comprises anopen-ended, water-cooled, vertically oscillating mold 10, a guideroll-rack 12, a bending-roll unit 13, a curved roll-rack 14, astraightener 15, and a run-out conveyor 16. Liquid metal is poured froma tundish 17 into the mold, and a partially solidified casting (notshown) emerges continuously from the bottom of the mold and travelssuccessively through the other aforementioned components. The machine isequipped with a flexible starter bar 18. The casting and starter bar arepropelled by speed-regulating drive rolls 20 and 20a in thestraightener, and by power driven pinch rolls in Nos. 1, 2 and 3auxiliary drives 21, 22 and 23 respectively, which are located at spacedlevels between the guide roll-rack 12 and the straightener 15 and arereversible. The other rolls are idlers.

The rolls of the bending-roll unit 13, the curved roll-rack 14 andauxiliary drives 21, 22 and 23 are arranged in top and bottom clusters24 and 25 of two rolls per cluster. Reference may be made to theaforementioned Bode and Wrhen patent for a detailed showing of thecluster construction. The work-engaging faces of the rolls of the bottomclusters 25 are intended to lie on a circular arc, the center ofcurvature of which is indicated at O and the constant radius at R. Thegap between the work-engaging faces of the top and bottom roll-pairs isindicated at G. Again for purposes of illustration only, we assume thatthe radius R is 30 feet, the gap G is 7.25 inches, all rolls of thecurved roll-rack are 12 inches in diameter, and the length of the chordbetween the axes of two adjacent rolls in the bottom clusters is 14inches. The length of the chord between the work-engaging faces of thesame rolls of course is a fraction of an inch smaller.

CONSTRUCTION OF APPARATUS

As shown in FIGS. 2 and 3, our apparatus for locating improperlypositioned or bent rolls comprises a housing 26 formed of metal platesand shaped essentially as a rectangular parallelepiped. The housingcarries a pair of straight parallel smooth-faced relatively fixedrunners 27 projecting from the outside face of its back wall. Thehousing contains a pair of base members 30 fixed to the inside face ofits back wall. Each base member carries a respective pair of pivot ears31 fixed to its mid-portion, and a respective pair of fluid-pressurecylinders 32 fixed to its opposite end portions. Respective straightparallel smooth-faced extensible runners 33 are carried by each pair ofpivot ears. Runners 33 have slots 34 which receive pins 35 mounted inthe ears, whereby the runners can pivot or move in-and-out with respectto the ears. Cylinders 32 have buttons 36 which engage runners 33 andurge the runners outwardly with respect to the housing. Tension springs37 are connected between the end portions of runners 33 and base members30 to hold the runners in contact with buttons 36. Suitable connections38 are mounted on the upper end wall of housing 26 for introducing fluidto cylinders 32. The front wall of the housing has a pair of slots 39through which runners 33 project.

The lower end wall of housing 26 carries a plurality of downwardlyprojecting hooks 42 adapted to engage a rung 43 at the top of thestarter bar 18. This is the rung which, at the beginning of a castingoperation, is used for attaching a chill plate to the starter bar.Preferably lock plates 44 are removably bolted to hooks 42 to preventunintended disengagement of the hooks from the rung, but to allowlimited freedom of movement. The upper end of housing 26 carries a pairof lifting eyes 45.

When we use the apparatus with a continuous-casting machine of theconstruction shown in FIG. 1, we connect the housing 26 to the top ofthe starter bar 18. We operate the various driven rolls of the castingmachine to move the housing through the path of travel defined by therolls of both the curved roll-rack 14 and the straight guide roll-rack12, first upwardly and then downwardly, to check the roll positions. Thefixed runners 27 abut the work-engaging faces of the bottom rolls of thecurved roll-rack and of the rolls at the left of the guide roll-rack,while the extensible runners 33 are urged into abutting relation withthe work-engaging faces of the top rolls and of the rolls at the right.The runners serve to guide the housing as it moves along the pathdefined by the rolls. The straight lengths of the runners aresufficiently short that, as the housing moves through the curvedroll-rack, the runners cannot abut simultaneously the work-engagingfaces of more than two top rolls and two bottom rolls. In the presentexample this length is about 23 inches. Hence whenever the runners abuttwo rolls each of the curved roll-rack, they lie on the chord of the arcon which the work-engaging faces of the rolls lie.

GAP MEASUREMENT

As best shown in FIGS. 2 and 4, the housing 26 contains a pair of gapsensors 48 located near its upper end near its respective side walls formeasuring the gap near each end of each roll pair. We may include morethan two gap sensors if we wish to measure gaps at other locations alongthe length of the rolls, for example at the mid-points. The gap sensorsare all of like construction; hence we describe only one. The gap sensor48 includes a tube 49 which is fixed to housing 26 and extends acrossits width. Back and front heads 50 and 51 are mounted within tube 48 forrelative movement axially of the tube or normal to the direction oftravel through path defined by the rolls. The tube has fixed stops 52and 53 near its opposite ends for engagement by shoulders 54 and 55 onthe heads 50 and 51 respectively to limit outward movement of the heads.The back head 50 has a bore 56 within which we mount a tubular fixture57. A compression spring 58 encircles the fixture 57 and bearsthereagainst and against the front head 51 to urge the two heads apartto the extent permitted by the stops 52 and 53. In their fully extendedpositions the heads 50 and 51 project slightly beyond the respectivefixed and yieldable runners 27 and 33.

A transducer 61 is mounted within the bore of the fixture 57. Acooperating wiper 62 is mounted on the end of the front head 51 andextends into the transducer. The transducer and wiper per se are knownitems available commercially; hence we have not shown nor described themin detail. One example of a suitable transducer and wiper combination wehave used successfully is available from Bournes, Inc., Riverside,California, under the designation "D.C. SN 0773-113". Electric leads 63from the transducer extend out the upper end of the housing 26 through afitting 64 to a suitable recorder 65 (shown only schematically in FIG.5). The recorder likewise is a known item available commercially. Oneexample of a suitable recorder we have used successfully with ourapparatus equipped with two gap sensors is available from SoltecCorporation, North Hollywood, California under the designation"B-261/LA/RC Flat Bed 2-Pen Recorder". We of course use a recorder whichhas at least as many pens as the number of gap sensors in the apparatus.Alternatively the signals may be fed to a computer for storage andmanipulation.

As shown schematically in FIG. 5, the gap-measuring circuit includespotentiometers 66 embodied in the respective transducers 61, and zeropotentiometers 67 for the respective transducers connected in parallelacross lines 68 and 69. The various potentiometers are connected to theaforementioned recorder 65, as indicated. We set the zero potentiometersso that the recorder reads "zero" when the heads 50 and 51 of each gapsensor are spaced apart by a predetermined distance relatively close tothe proper gap. In the present example we may set the "zero" at 7inches. The zero setting is needed to bring the recorder into the properscale. As we use the apparatus to measure gaps, signals transmitted bythe transducer potentiometers to the recorder 65 are indicative ofdifferences between the actual gap measurement and the zero setting.

As we move the apparatus through the path defined by the rolls, theheads 50 and 51 of the gap sensors 48 sucessively contact thework-engaging faces of each roll-pair in turn. As the sensors movebeyond each pair of work-engaging faces, the heads move outwardly underthe action of springs 58. The voltage signals from the transducersincrease in magnitude as the heads move closer together. The signal isminimum while the sensors are out of contact with rolls and maximum whenthe heads contact the work-engaging faces of the rolls. The maximumsignal at each roll pair is representative of the gap. FIG. 6 isrepresentative of the form of recording which results. This is an actualrecording obtained with our apparatus equipped with three gap sensors(one in the middle in addition to the two near opposite sides as shownin FIGS. 2 and 3).

ANGLE MEASURMENT

As shown in FIG. 2, the apparatus includes a pair of angle sensors 70located inside the opposite side walls of the housing 26 midway of theheight. Preferably the angle sensors are mounted on separate plates 71which underlie the respective side walls of the housing and project fromthe back face of the housing. Springs 72 urge the plates 71 outwardly tothe extent permitted by stops 73 (FIG. 4). Thus the plates serve asadditional runners which are spring loaded. The angle sensors per se arependulum devices of a known construction available commercially. Oneexample of a suitable device we have used successfully is available fromHumphrey, Inc., San Diego, California, under the designation "CP49-Precision Pendulum Potentiometric Transducer". We have not shown ordescribed the device in detail, but FIG. 7 illustrates the principleinvolved. The sensor includes a pendulum 74 and a potentiometer 75 whichwe connect to lines 76 and 77.

As the housing 26 moves through the roll-rack 14, the roll-engagingedges of the spring-loaded runners 71 always lie at the same angle tothe horizontal as a line tangent to the two bottom rolls abutted bythese runners. The pendulum 74 always assumes a vertical position.Consequently an angle X between the tangent line and the pendulum is thecomplement of the angle which the tangent line makes with thehorizontal. The pendulum support serves as a wiper for the potentiometer75, which transmits voltage signals to a digital recorder 78. Thecircuit includes a zero potentiometer 79, which in this instance we canset to zero. We can calibrate in either direction, but the magnitude ofthis signal varies directly with the size of the angle X. The digitalrecorder per se is a known item available commercially. One example of asuitable digital recorder we have used successfully is available fromPractical Automation, Inc., Shelton, Connecticut, under the designation"PDM-711 21 19,999 NDC Printing DVM". Since the angle measurementsinvolve very small increments, we require a recorder which affordsfour-digit resolution or a computer.

We calculate beforehand the size of angle which a line tangent to eachpair of adjacent rolls should make with the horizontal. In the presentexample the work-engaging faces of the rolls lie on arcs of constantradii and each cluster occupies an arc which measures 4°22'50". If everybottom roll is positioned correctly, the angle which each tangent linemakes to the horizontal is greater by a uniform increment than the anglewhich the next lower tangent line makes with the horizontal. If ourapparatus is moved through the curved roll-rack from the lower end up,each successive measurement of the horizontal angle should increase bythis amount from 0° to 90°. Exactly halfway up a curved roll-rack ofconstant radius, the angle should measure 45°. In some curved roll-racksthe radii of show arcs on which the work-engaging faces lie vary alongcontinuous-casting length of the rack, but the proper horizontal angleof lines tangent to these faces always can be determined.

FIG. 8 illustrates the geometric principle involved in using themeasurement of the angle to determine whether the work-engaging faces ofthe bottom rolls lie on an arc of the intended radius. The figure ismuch exaggerated from the actual scale of a curved roll-rack. FIG. 8shows two successive rolls 80 and 81, the work-engaging faces of whichare intended to lie on an arc A of radius R. For simplicity we assumethat the line T tangent to the work-engaging faces of these rolls isintended to lie at an angle of 45° to the horizontal, and that the roll80 already has been positioned properly. If the roll 81 is improperlypositioned too close to the center of curvature O, as indicated indotted lines in FIG. 8, the distance between the center of curvature andits work-engaging face is the shorter radius R₁. The resulting tangentline T₁ makes a greater angle with the horizontal than the desiredtangent line T, and the complement of this angle measures too low, 35°in FIG. 8.

In applying the foregoing principle, we known that the line tangent totwo rolls at the exit end of the curved roll-rack should be horizontal.We position these lowermost bottom rolls properly, as with a level. Nextwe use our apparatus to determine whether the succeeding bottom roll upthe rack is positioned properly, and if necessary correct its positionby adding or removing shims. In similar fashion we correct the positionof each bottom roll up the rack, each time relying on the next lowerroll having already been positioned properly. In the example, wedetermine the angle when the angle sensor reaches a position exactlymidway between each two clusters and again when it reaches a positionexactly midway of each cluster. If the bottom rolls are positionedproperly and the gaps are correct, the top rolls automatically arepositioned properly.

LOCATING BENT ROLLS

To locate bent rolls, we move our apparatus first in one directionthrough the path defined by the rolls and then in the oppositedirection. In the continuous-casting machine illustrated, we normallymove the apparatus first upwardly and then downwardly. The heads 50 and51 of the gap sensors 48 can be expected to contact each roll at adifferent location on its circumference on each pass. Consequently bentrolls are indicated whenever the gap measurements on the downward passdiffer from the measurements on the upward pass. If the apparatus has athird gap-sensor at its mid-point a bent roll may be indicated by asignificant difference between the gap measurement at mid point and atthe ends without need for a second pass.

OPERATION

To summarize the operation of our apparatus, we move the housing 26along a confined path defined by sets of roll-pairs. If the roll-pairsare in a roll-rack of a continuous-casting machine which employs aflexible starter bar 18, we connect the housing to the upper end of thebar by engaging the hooks 42 with the rung 43 of the bar. In othermachines (for example, a continuous-casting machine equipped with arigid starter bar) we may engage the lifting eyes 45 with a suitablehoisting mechanism and pull the housing up the path. Preferably we movethe housing up the path and back down, measuring the gaps and the anglesas the housing moves in both directions to locate bent rolls, and alsoas a check. The measurements recorded on the recorder 65 show the gap ateach roll-pair. The angular measurements obtained on the digitalrecorder 78 shown whether the work-engaging faces of the bottom rollslie on an arc of the intended radius in the example of a curvedroll-rack.

We have illustrated an apparatus which embodies both gap sensors andangle sensors. Nevertheless it is apparent we can employ the sameprinciples in an apparatus which embodies only gap sensors or only anglesensors without the other.

From the foregoing description it is seen that our invention affords asimple advantageous method and apparatus for measuring the gaps betweenthe work-engaging faces of rolls which define a confined path of travelfor a workpiece. The invention also facilitates determining whetherthese faces lie on arcs of the intended radii. Once these determinationshave been made, it is of course a simple matter to insert or removeshims and thus position the rolls correctly. If bent rolls are located,they can be replaced.

We claim:
 1. An apparatus for locating improperly positioned rolls amonga set of rolls which are arranged in opposed pairs and havework-engaging faces defining a confined path of travel for a workpiece,said apparatus comprising a housing movable along said path, meanscarried by said housing at opposite faces thereof for abutting saidwork-engaging faces and guiding said housing, and a plurality of gapsensors carried by said housing and including heads supported forrelative movement normal to the direction of movement of said housingalong said path and adapted to contact the work-engaging faces of theindividual roll-pairs successively at a plurality of locations along thelength of the rolls, and transducer means operatively connected withsaid heads for transmitting signals representative of the measurementsof the gaps between the work-engaging faces of each roll-pair contactedby said heads.
 2. An apparatus as defined in claim 1 in which the meansfor guiding said housing includes relatively fixed runners projectingfrom one face of said housing, extensible runners projecting from theopposite face of said housing, and means within said housing urging saidextensible runners outwardly with respect to said housing.
 3. Anapparatus as defined in claim 2 in which said extensible runners aresupported in said housing for pivotal and in-and-out movement, and themeans urging said extensible runners outwardly includes fluid-pressurecylinders mounted in said housing, means operated by said cylindersbearing against said extensible runners, and spring means connected withsaid extensible runners holding them in contact with said cylinderoperated means.
 4. An apparatus as defined in claim 1 in which saidhousing is movable in two directions along said path, whereby differentgap measurements obtained as said housing moves in opposite directionsindicate bent rolls.
 5. An apparatus as defined in claim 1 comprising inaddition angle-measuring means for transmitting signals representativeof the angles of lines tangent to the work-engaging faces of adjacentrolls and thereby indicating whether the work-engaging faces lie on anarc of a predetermined radius.
 6. An apparatus as defined in claim 5 inwhich said angle-measuring means includes a pendulum device andtransducer means operatively connected with said pendulum device.
 7. Anapparatus as defined in claim 1 comprising in addition means at one endof said housing for attaching said housing to a starter bar of acontinuous-casting machine.
 8. An apparatus as defined in claim 7 inwhich said starter-bar attaching means includes a lock which permitslimited freedom of movement of said housing with respect to the starterbar.
 9. An apparatus as defined in claim 1 comprising in additionlifting eyes at one end of said housing for attaching a hoistingmechanism to pull the housing along the path defined by the folls. 10.An apparatus for locating improperly positioned rolls in a curbedroll-rack, the rolls of which are arranged in opposed pairs and havework-engaging faces defining a confined path of travel for a workpieceand lying on arcs of predetermined radii, said apparatus comprising ahousing movable along said path, at least one gap sensor carried by saidhousing for transmitting signals representative of the gap measurementbetween the rolls of the various pairs, and angle-measuring meanscarried by said housing for transmitting signals representative of theangles of lines tangent to work-engaging faces of adjacent rolls andthereby indicating whether the work-engaging faces lie on arcs of theintended radii.
 11. An apparatus as defined in claim 10 comprising aplurality of gap sensors for transmitting signals representative of thegaps between rolls at a plurality of locations along the length of therolls.
 12. An apparatus as defined in claim 10 comprising in additionrunners carried by said housing and projecting from opposite facesthereof for abutting the rolls of the opposed pairs and guiding saidhousing as it moves along said path.
 13. An apparatus as defined inclaim 12 in which the runners projecting from one face of said housingare fixed relative thereto and the runners projecting from the otherface of said housing are extensible, and comprising in addition meanswithin said housing urging said extensible runners outwardly withrespect to said housing.
 14. An apparatus as defined in claim 10 inwhich said gap sensor includes heads supported for relative movementnormal to the direction of movement of said housing along said path andadapted to contact the work-engaging faces of the individual roll-pairsalong said path, and transducer means operatively connected with saidheads.
 15. An apparatus as defined in claim 10 in which said housing ismovable in two directions along said path whereby different gapmeasurements obtained as said housing moves in opposite directionsindicate bent rolls.
 16. An apparatus as defined in claim 10 in whichsaid angle-measuring means includes a pendulum device and transducermeans operatively connected with said pendulum device.
 17. An apparatusas defined in claim 10 comprising in addition means at one end of saidhousing for attaching said housing to a starter bar of a continuouscasting machine.
 18. An apparatus for locating improperly positionedrolls in a curved roll-rack in which the rolls are arranged in opposedpairs and have work-engaging faces lying on arcs of predetermined radii,said apparatus comprising a housing movable through the roll-rack, guidemeans on said housing adapted to abut two adjacent rolls and lie on aline tangent to the work-engaging faces thereof, and angle-measuringmeans in said housing for indicating the angle at which said guide meanslies and thereby indicating whether the work-engaging face of each rolllies on an arc of the intended radius.
 19. An apparatus as defined inclaim 18 in which said angle-measuring means includes a pendulum deviceand transducer means operatively connected with said pendulum device fortransmitting signals representative of the angle.
 20. An apparatus asdefined in claim 18 comprising in addition at least one gap sensormounted in said housing for transmitting signals representative of themeasurement of the gaps between the rolls of the various roll-pairs. 21.The combination, with a continuous-casting machine which includes acurved roll-rack, a flexible starter bar, and drive means for propellingsaid starter bar through said roll rack, of an apparatus attached tosaid starter bar for locating improperly positioned rolls in said rollrack, said apparatus being constructed as defined in claim
 1. 22. Amethod of locating improperly positioned rolls among a set of rollswhich are arranged in opposed pairs and have work-engaging facesdefining a confined path of travel for a workpiece, said methodcomprising moving an apparatus along said path, transmitting signalsfrom said apparatus, representative of the measurement of the gapseparating the work-engaging faces of rolls of each pair in successionat a plurality of locations along the length of the rolls during eachpass of the apparatus along said path, and recording said signals.
 23. Amethod as defined in claim 22 comprising the further step of moving saidapparatus along said path in two directions to obtain signals indicativeof bent rolls.
 24. A method as defined in claim 22 in which said set ofrolls is a curved roll-rack, and said apparatus is attached to a starterbar to be moved along said path.
 25. A method of locating improperlypositioned rolls among a set of rolls which are arranged in opposedpairs and have work-engaging faces defining a confined path of travelfor a workpiece, said method comprising moving an apparatus along saidpath, transmitting signals from said apparatus representative of themeasurement of the gap separating the work-engaging faces of rolls ofeach pair in succession, transmitting signals representative of theangles of lines tangent to each adjacent pair of work-engaging faces,and recording both the gap-measurement signals and the angle-measurementsignals.
 26. An apparatus for locating improperly gapped rolls among aset of rolls arranged in opposed pairs and having work-engaging faceswith a gap therebetween defining a confined path of travel for aworkpiece, said apparatus comprising a supporting structure, meanscarried by said structure for contacting the work-engaging faces of eachpair of rolls at opposite sides of the gap and thereby guiding thestructure as it moves along said path, a plurality of gap-sensing meanscarried by said structure for measuring the gap between each pair ofrolls in succession at a plurality of locations along the length of therolls, and means connected with said gap-sensing means for transmittingsignals representative of the measurements.
 27. An apparatus as definedin claim 26 comprising in addition means on the lower end of saidstructure for attaching the apparatus to a starter bar of acontinuous-casting machine enabling the apparatus to be propelled withthe starter bar through roll-racks of a continuous-casting machine..Iadd.
 28. A measuring device for measuring the separation distancebetween conveying rollers in the secondary cooling zone of continuouscasting machines comprising transport means adapted to be guided throughsaid cooling zone between said rollers, said transport means having amaximum dimension parallel to said separation distance which is lessthan said distance and at least one distance detecting means mounted onsaid transport means for movement therewith, said distance detectingmeans including at least one probe projecting beyond the limits of saidtransport means for engagement with a roller, said probe beingdisplaceably supported on said transport means and providing an outputsignal corresponding in magnitude to the extent of said displacementwhereby upon movement of said transport means through said zone, saidsignal provides an indication of variations in said separation distancealong said zone. .Iaddend..Iadd.
 29. The measuring device of claim 28wherein said distance detecting means includes two oppositely projectingprobes arranged in close proximity to one another, whereby the combinedsignals from said probes indicates the extent of said separationdistance at any given point in said zone. .Iaddend..Iadd.
 30. The deviceof claim 28 wherein said distance detecting means is yieldable supportedon said transport means to permit bodily retraction where the limit ofthe tolerable displacement is exceeded. .Iaddend. .Iadd.
 31. The deviceof claim 28 wherein said distance detecting means includes twooppositely projecting probes arranged coaxially. .Iaddend.